Abstract Objectives: to evaluate and identify the prevalence of interruption of breastfeeding (BF) in the period of up to 45 days postpartum and the associated sociodemographic and obstetric factors. Methods: cohort of 622 puerperal women, selected between 2018 and 2019 in a reference maternity hospital in the South Brazil. Data collection was carried out in two phases, the first in the maternity hospital during hospitalization of the puerperal woman and the newborn and the second through a telephone call, which occurred 60 days after birth. Poisson regressions with robust variance were performed to identify the factors associated with interruption of BF in the first 45 days of life. The variables that presented p<0.20 in the crude analysis were included in the adjusted analysis. Results: the interruption of BF at 45 days was identified in 14% of the sample. Higher maternal age (PR= 0.46; CI95%= 0.22-0.93), eight years or less of education (PR= 2.11; CI95%= 1.05-4.25), support from the maternal grandmother (PR= 1.91; CI95%= 1.20-3.06) and receiving complement at the maternity hospital (PR= 1.53; CI95%= 1.04-2.25) were factors related to the interruption of BF in the 45-day postpartum period. Conclusion: maternal age ≥35 was a protective factor, and less education, the support of the maternal grandmother and receiving complement at the maternity hospital were predictors of early breastfeeding abandonment.